REPRODUCTION 



189 



occurrence of both sexes in the same individual, is almost 

 as much the exception in the animal world as it is the 

 rule in the vegetable world. It might be reasonable 



FIG. 80. Withdrawal and deposition of pollinia in the flowers of an orchid. 

 Flowering spike of the broad-leaved helleborine (Epipactis latifolia) upon which 

 a wasp (Vespa austriaca) is alighting. 2, A flower of the same seen from the 

 front; 3, side view of the same flower with the half of the perianth toward the 

 observer cut away; 4, the two pollinia joined by the sticky rostellum; 5, the 

 same flower being visited by a wasp, which is licking honey and at the same 

 time detaching with its forehead the tip of the rostellum together with the pair 

 of pollinia; 6, the wasp leaving the flower with the pollinia cemented to its head, 

 the pollinia are erect; 7, the wasp visiting another flower and pressing its fore- 

 head with the pollinia (which in the meantime have bent down) against th 

 stigma. (Kerner and Oliver.) 



to regard this difference as referable to the prevailing 

 restriction of movement among plants, as contrasted 

 with the freedom of movement among animals, making it 

 correspondingly difficult or easy for different individuals 



